1. Field of Art
The present invention relates to a pulse detecting equipment for detecting pulses aircraft 6 has transmitted or received to grasp its location.
2. Description of Relevant Art
Flying aircraft determines the location in a variety of manners, including the method of using a DME (distance measuring equipment), refer to Japanese patent application Laid-Open Publication No. 2009-14398.
The DME is installed as equipment on the ground, as illustrated in FIG. 1. It receives pulses transmitted from aircraft 6, and transmits to aircraft 6 pulses responding the received pulses. The aircraft 6 determines its flying location using pulses transmitted to and received from a first, a second, or a third DME 5a, 5b, or 5c (referred herein to collectively as a DME 5).
FIG. 2 shows as an example a pair of interrogation pulses P1 transmitted from aircraft 6. Having received interrogation pulses P1 transmitted from aircraft 6, the DME 5 works, with lapse of a predetermined time (Td) after the reception of interrogation pulses P1, to transmit reply pulses P2 responding the interrogation pulses P1. Having received reply pulses P2 transmitted from the DME 5, the aircraft 6 is measuring a distance from the DME 5 to the aircraft 6 depending on a propagation velocity of electric waves (as a signal) and a response time T determined from combination of a transmission time t1 of interrogations pulses P1 and a reception time t2 of reply pulses P2.
Such interrogation pulses P1 as well as reply pulses P2 are paired as twin pulses in compliance with an international prescript per mode of operation, covering the pulse spacing, delay interval, etc, cf. refer to “Aeronautical Telecommunications, ANNEX10, VOLUME I” issued from the ICAO, Jul. 1996, pp. 27-40).
For instance, for the DME/N mode, interrogation pulses P1 as well as reply pulses P2 have a pulse width of 3.5 μs, and a pulse spacing of 12 μs. For respective DMEs 5, frequencies of pulses to be transmitted and received are individually prescribed. In the example of FIG. 1, the first DME 5a has a frequency of reception pulses prescribed as 961 MHz, the second DME 5b, a frequency of reception pulses prescribed as 960 MHz, and the third DME 5c, a frequency of reception pulses prescribed as 962 MHz.
The first DME 5a is adapted, as illustrated in FIG. 3, to reply simply to reception of interrogation pulses P1 within a range about a prescribed frequency (961 MHz), and not to respond interrogation pulses P1 to neighboring channels (960 MHz, 962 MHz) even upon reception of any them. In other words, the DME 5 is configured to detect interrogation pulses P1 within a prescribed frequency range from among received signals, and transmit reply pulses P2 within a prescribed frequency range. It is noted FIG. 1 shows values of frequencies designated for reception of interrogation pulses P1, which are different from frequencies designated for reply pulses P2.
(Analog System)
Accordingly, the DME 5 is provided with a pulse detecting equipment mounted thereto for detecting interrogation pulses P1 transmitted from aircraft 6 to own equipment.
FIG. 4 shows a typical pulse detecting equipment 2 of analog system as an example, which includes: an RF (Radio Frequency) amplifier 202 for amplifying signals (RF (Radio Frequency) signals) received at an antenna 201; a mixer 204 for mixing received signals with RF signals of a prescribed frequency output from an oscillator 203, to provide IF (Intermediate Frequency) signals; a first filter 205 for limiting a frequency band of signals input from the mixer 204, to a first frequency band (900 kHz); a second filter 206 for limiting a frequency band of signals input from the mixer 204, to a second frequency band (150 kHz); a first diode detector 207 for wave detection of signal levels of signals input from the first filter 205; a second diode detector 208 for wave detection of signal levels of signals input from the second filter 206; a comparator 209 for comparison between signals detected at the diode detector 207 and 208; and a pulse detector 210 employing results of comparison of the comparator 209, to detect interrogation pulses P1 transmitted to own equipment. Afterward, the DME 5 provided with the pulse detecting equipment 2 works to generate, to transmit to aircraft 6, reply pulses P2 responding to interrogation pulses P1 detected by the pulse detecting equipment 2.
The pulse detecting equipment 2 of analog system has internal circuitry of analog system, including the first filter 205 and the second filter 206 as analog circuit components difficult in adjustments for characteristic balances, as a problem. Even of a sort, analog circuit components have different characteristics by individual components, with the need of selecting a balanceable component from among given components. Further, analog components are subject to deterioration, with anxieties that the filters 205 and 206, even if initiated with balanced characteristics, might lose characteristic balances during a service, affecting pulse detection.
(Digital System)
To solve the problem in analog system the filters 205 and 206 might suffer in adjustment of characteristic balance, there are pulse detecting equipments of digital system free of adjustments of the filters 205 and 206.
FIG. 5 shows a typical pulse detecting equipment 3 of digital system as an example, which includes: an RF (Radio Frequency) amplifier 32 for amplifying signals (RF (Radio Frequency) signals) received at an antenna 31; a mixer 34 for mixing received signals with RF signals of a prescribed frequency output from an oscillator 33, to provide IF signals; a high-level signal processor 35 for processing high-level signals; a low-level signal processor 36 for processing low-level signals; a comparator 37 for comparison between signals wave-detected at the high-level signal processor 35 and signals wave-detected at the low-level signal processor 36; and a pulse detector 38 employing results of comparison of the comparator 37, to detect interrogation pulses P1 transmitted to own equipment.
This pulse detecting equipment 3 is employed for detection of interrogation pulses P1 transmitted from aircraft 6, and is required to cope with signal levels (amplitude levels) of interrogation pulses P1. On the other hand, AD (Analog Digital) converters are subject to restriction to signal levels they can cope with, so it is impractical to use an AD converter for processing a range of signals covering from high level signals to low level signals received from aircraft 6, without adjusting their levels. However, adjusting levels of signals may change frequencies of some signals. Accordingly, the pulse detecting equipment 3 is configured at the high-level signal processor 35 for processing received signals of high levels within a working range of an AD (Analog Digital) converter 352, and at the low-level signal processor 36 for processing received signals of low levels within a working range of an AD (Analog Digital) converter 362, in a separately processing manner, to combine respective results together for detection of interrogation pulses P1, permitting interrogation pulses P1 to be detected with maintained frequency information.
The high-level signal processor 35 is configured with: an adjuster 351 for adjustment in level (amplification or attenuation) of signals input from the mixer 34; the above-noted AD converter 352 for conversion of level-adjusted high-level signals (that can be processed within an unsaturated working region of the AD converter with standard-compliant maximum power) from analog signals to digital signals; a down-converter 353 for conversion to down-convert digitalized signals into complex data (IQ (In phase Quadrature phase) data); a first filter 354 for limiting a frequency band of signals converted into IQ data, to a first frequency band (900 kHz); a second filter 355 for limiting a frequency band of signals converted into IQ data, to a second frequency band (150 kHz); a first detector 356 for wave detection of levels of signals input from the first filter 354; and a second detector 357 for wave detection of levels of signals input from the second filter 355.
Likewise, the low-level signal processor 36 is configured with: an adjuster 361 for adjustment in level (amplification or attenuation) of signals input from the mixer 34; the above-noted AD converter 362 for conversion of level-adjusted low-level signals (that can be detected at standard-compliant minimum power) from analog signals to digital signals; a down-converter 363 for conversion to down-convert digitalized signals into complex data (IQ data); a first filter 364 for limiting a frequency band of signals converted into IQ data, to a 900 kHz frequency band; a second filter 365 for limiting a frequency band of signals converted into IQ data, to a 150 kHz frequency band; a first detector 366 for wave detection of levels of signals input from the first filter 364; and a second detector 367 for wave detection of levels of signals input from the second filter 365.
Accordingly, the high-level signal processor 35 is adapted to accurately detect simply high-level signals to output, and inadaptable for accurate detection of low-level signals. On the other hand, the low-level signal processor 36 is adapted to accurately detect simply low-level signals to output, and inadaptable for accurate detection of high-level signals that become saturated.
Therefore, the comparator 37 comparing signals input form the detectors 356, 357 and 366, 367 is adapted to work, if the reception signal is a high level, to output to the pulse detector 38 an input signal from the high-level signal processor 35, and if the reception signal is a low level, to output to the pulse detector 38 an input signal from the low-level signal processor 36.
By provision of the pulse detecting equipment 3 of digital system, the DME 5 can detect interrogation pulses P1 transmitted to own equipment, and generate reply pulses P2 responding interrogation pulses P1 to own equipment, to transmit to aircraft 6.
However, for a dynamic range (a necessary range for adaptation to low and high signal levels) to be secured, the pulse detecting equipment 3 of digital system needs a pair of processors being the high-level signal processor 35 and the low-level signal processor 36, with a complicated equipment configuration, as a problem.
As described, the pulse detecting equipment 2 of typical analog system includes a combination of first analog filter and second analog filter difficult of adjustment, as a problem. On the other hand, the pulse detecting equipment 3 of digital system needs a complicated equipment configuration, as a problem.
To this point, it is an object of the present invention to provide a pulse detecting equipment with a simplified equipment configuration allowing for facilitated pulse detection.